Prepared by Marjan Kluepfel, HGIC Horticulture Specialist, and Bob Polomski, Extension Consumer Horticulturist, Clemson University. (New 05/99. Images added 04/09.)
Gardenias are popular shrubs in South Carolina. They are not the easiest shrubs to grow, but the exquisite white, fragrant flowers make up for the extra attention gardenias require.
Double flowered gardenia blossom
Karen Russ, ©2008 HGIC, Clemson University
Gardenia jasminoides or Common Gardenia or Cape Jasmine is an evergreen shrub, which grows to a height of 2 to 6 feet, depending on the variety. Spread is about the same. The foliage of well-fed shrubs is glossy, dark-green, 2 to 4 inches long and half as wide. Depending on the cultivar, the flowers can be either single or double and up to 4 inches in diameter. They are waxy, white and very fragrant.
The growth rate is medium.
Gardenias are primarily grown for their fragrant flowers and handsome foliage. They should be planted where people will notice the fragrance. The flowers open over a long period of time, from May through July.
Single flowered gardenia blossom,
Flickr: Nemo's great uncle Creative Commons license 2.0
Gardenias require considerable maintenance. Fall or spring is the best time for planting. Plant in light to moderate shade, preferably with minimum competition from tree roots. Gardenias resent root disturbance. They also grow well in pots.
Gardenias prefer acid, moist, well-drained soils. Add plenty of organic matter, such as compost or ground bark, to as large an area as possible. Mulch plants instead of cultivating. A good time to feed gardenias is mid-March, using an acid plant food, fish emulsion or blood meal. Feed the shrubs again in late June to encourage extra flowers on everbloomers or faster growth of young shrubs. Do not fertilize gardenias in the fall. Doing so will stimulate tender growth, which may be killed if the temperature in winter drops below 15 degrees. Gardenias are cold-sensitive and during severe winters can be killed to the ground in the Upstate. Often they regenerate in spring.
Prune shrubs after they have finished flowering to remove straggly branches and faded flowers. Water gardenias regularly. Drip-irrigating the shrubs will keep water off the foliage and blossoms and prevents leaf spots. Regular watering is necessary after blooming also to keep the plants in good condition and able to withstand winter weather.
Gardenia "hips" (fruit) occasionally appear in fall
Karen Russ, ©2008 HGIC, Clemson University
Several insects and diseases are likely to show up on your gardenia. When sooty mold coats gardenia leaves in summer, it is usually due to an infestation of whiteflies. These sucking insects look like bits of cotton. While eating, they excrete excess moisture in the form of honeydew and this, in turn, supports the growth of a black fungus. Similar in habit are small gray aphids, which cling to leaf undersides. In sandy soil, nematodes can cause gardenias to be stunted or even die. Nematodes are microscopic worms, which live in the soil and feed on plant roots. Root rots caused by several different fungi can also be a problem, especially in poorly drained soils.
Another problem encountered is "bud drop." Flower buds abort and drop off just before they open. Common causes include low humidity, overwatering, underwatering, insufficient light and high temperatures (night temperatures between 50 and 55 °F are necessary for the formation of flower buds).
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This information is supplied with the understanding that no discrimination is intended and no endorsement of brand names or registered trademarks by the Clemson University Cooperative Extension Service is implied, nor is any discrimination intended by the exclusion of products or manufacturers not named. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.